Power Thickness of Laser Cutting: A Working Comparison
This page compares the power thickness of laser cutting for stainless steel, carbon steel, aluminum alloy and brass. It is written for engineers and buyers who must choose between a 1.5 kW fiber source, a 6 kW, a 12 kW, or a CNC milling process for the same part. Read it and you can set a power level and a plate range without guessing.
In this article
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Power thickness of laser cutting by material
Typical single-pass limits with oxygen or nitrogen assist. Real limits move with gas purity, nozzle condition and the edge quality you need.
| Source power | Carbon steel | Stainless steel | Aluminum / brass |
|---|---|---|---|
| 1.5 kW | up to 6 mm | up to 4 mm | up to 3 mm |
| 3 kW | up to 12 mm | up to 8 mm | up to 6 mm |
| 6 kW | up to 20 mm | up to 12 mm | up to 10 mm |
| 12 kW | up to 30 mm | up to 25 mm | up to 20 mm |
Fiber laser vs. CNC milling for the same plate
Use this when the question is not which wattage, but which process should own the part.
| Factor | Fiber laser | CNC milling |
|---|---|---|
| Edge finish | Ra 3.2–12.5 μm, oxide on rim | Ra 0.8–1.6 μm as machined |
| Tolerance on profile | ±0.1 mm typical | ±0.005 mm achievable |
| Holes under 2 mm | Limited, taper risk | Routine with drill or mill |
| Hardness change | Small heat-affected zone | None |
| Cost driver | Cut length and gas | Cycle time and setup |
| Best batch size | 1 to 10,000+ sheets | 1 to 10,000+ parts |
What actually limits plate thickness
Wattage is only the headline number. The depth a beam reaches depends on focus spot size, assist gas pressure, nozzle standoff and how fast the table can move without dross. A 6 kW source on 12 mm stainless with nitrogen at 16–18 bar cuts clean; the same head on 20 mm stainless needs slower feed and still leaves a rougher kerf.
Absorption is the second factor. Carbon steel absorbs the 1,070 nm fiber wavelength well once the melt is hot, which is why oxygen assist pushes carbon steel further than stainless at the same power. Aluminum and brass reflect a large share of the beam when cold, so pierce time grows and the practical ceiling drops by roughly one third against stainless.
Edge quality sets the real ceiling. If the drawing calls for Ra 0.8–1.6 μm and no oxide, laser cutting stops being viable well before the machine stops cutting. At that point the part moves to milling, where the same geometry is finished in one setup.
- 1Gas matters as much as wattsNitrogen gives a clean stainless edge; oxygen is faster and cheaper on carbon steel.
- 2Pierce time dominates thin-gauge workOn 1–3 mm sheet, pierce and travel time, not power, set the cycle.
- 3Reflective metals need careBrass and copper can damage optics if the pierce is not controlled.
Stainless, carbon steel, aluminum and brass compared
Carbon steel is the friendliest material for a fiber source. A 3 kW unit holds 12 mm with oxygen assist at a reasonable feed, and 6 kW reaches 20 mm. Above 20 mm, cut quality drops fast: the kerf widens, dross builds on the bottom edge and the parts usually need a second operation anyway.
Stainless steel 304 and 316 cut cleanly with high-pressure nitrogen. A 6 kW source manages 12 mm, and 12 kW reaches roughly 25 mm in production. Thicker sections are possible on paper, but the heat-affected zone and the nitrogen bill both rise, so most shops quote 20 mm as the practical line.
Aluminum alloy 6061 and 5052 reflect the beam and conduct heat away quickly, so you lose about a third of the stainless thickness at every power level. Brass behaves in a similar way and demands a controlled pierce to protect the optics. Below 3 mm both cut fast; above 10 mm the burr and taper usually send the part to a mill.
- 1Carbon steelBest thickness-to-power ratio; 6 kW covers most job-shop work.
- 2Stainless 304 / 316Needs nitrogen; 6–12 kW for 8–20 mm production plates.
- 3Aluminum 6061 / 5052Plan for about two thirds of the stainless limit at the same wattage.
- 4Brass C27400 / C28000Thin gauges only; watch pierce control and lens protection.
Where laser cutting stops and machining starts
Holes are the first crossover point. A fiber laser can pierce a 3 mm hole in 6 mm steel, but the entry is wider than the exit. If the drawing calls for a 2 mm hole with a ±0.05 mm tolerance, the laser cannot hold it and the part should be milled or drilled after cutting.
Surface finish is the second. Cut edges carry a light oxide on carbon steel and a matte grey rim on stainless. Anodizing and plating both show that rim, so cosmetic parts go to machining, bead blasting or tumbling before finishing. Functional brackets rarely care.
Tolerance on large profiles is the third. Fiber laser holds roughly ±0.1 mm across a sheet, which is fine for panels and frames. When a mating bore needs ±0.005 mm, the plate is cut oversize and finished on a CNC mill. That hybrid route is common for 4,000 mm frames where one or two features need tight tolerance.
Volume changes nothing here. Laser wins on cut length; milling wins on feature count and tolerance. A part with forty small holes and two tight bores is usually cheaper as a milled part, even at high quantity.
- 1Cut oversize, then machineKeep laser for the outline and mill only the tight features.
- 2Count the featuresMany small holes or slots push the part toward milling.
- 3Check the finish specVisible or anodized edges usually rule out a raw laser kerf.
How to verify a power and thickness claim
Ask for the assist gas, not just the wattage. A 12 kW claim on 20 mm stainless means nothing if the cut ran on compressed air, since the edge will be oxidized and the tolerance loose. Nitrogen at 16–20 bar is the honest baseline for stainless and aluminum.
Ask for the feed rate and the edge photo. A cut table without a speed figure hides the trade: anyone can cut thick plate slowly. A usable quote lists material, thickness, gas, pressure, focus, speed and the measured Ra on the kerf.
Check the machine age and the optics service record. A 6 kW source with a worn nozzle and a dirty lens performs like a 3 kW unit. Nozzle diameter, lens condition and chiller stability explain more day-to-day variation than the nameplate rating.
- 1Gas and pressureNitrogen 16–20 bar for stainless; oxygen for carbon steel speed.
- 2Speed figureA thickness claim without a feed rate is marketing, not data.
- 3Edge photo at 10×Look for dross on the bottom and striations on the wall.
Which route to pick
For flat plates up to 12 mm stainless, 20 mm carbon steel or 10 mm aluminum with a ±0.1 mm profile tolerance, cut on a 6–12 kW fiber laser and save the setup cost. For holes under 2 mm, bores at ±0.005 mm, visible edges or anodized faces, cut the outline oversize and finish on a CNC mill. Brass and thick aluminum almost always belong in the second group.
Questions engineers ask next
Can a 1.5 kW fiber laser cut 6 mm stainless steel?
It can, but only slowly and with nitrogen at high pressure. The kerf will show striations and the edge will be rougher than a 6 kW result at the same thickness.
For anything above 4 mm stainless in production, a 3 kW source or higher is the safer quote.
Why does aluminum cut thinner than stainless at the same power?
Aluminum reflects a large part of the 1,070 nm beam when cold and conducts heat away from the kerf quickly. Both effects reduce the energy left for melting.
Expect roughly two thirds of the stainless thickness limit, and allow longer pierce times on 6061 and 5052.
Does laser cutting change the material properties?
A narrow heat-affected zone forms along the kerf. On carbon steel it can harden the edge slightly; on stainless it can leave a thin oxidized layer.
If the part is later welded or anodized, remove 0.05–0.1 mm from the cut face or switch to machining.
When is laser cutting cheaper than CNC milling?
When the part is flat, has few tight features and the profile tolerance is around ±0.1 mm. Cut length is the cost driver, so a long outline with few holes favors the laser.
A part with many small holes or two or three tight bores usually costs less as a milled part, because the laser would need a second operation anyway.
Can brass be cut on a fiber laser?
Yes, up to around 6–10 mm depending on power. Brass reflects the beam, so the pierce must be controlled and the lens protected.
Above that range, or when the edge will be visible, milling or waterjet is the lower-risk route.
Does plate thickness affect the achievable tolerance?
Yes. Thin sheet stays flatter and holds a tighter profile. As thickness grows, thermal distortion and dross increase the variation.
A ±0.1 mm profile is realistic up to about 12 mm; beyond that, plan for ±0.2 mm or finish the edge on a mill.
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